In an optical communication system, an optical module used for transmission/reception of an optical signal is embedded. In such optical module, a Mach-Zehnder type optical modulator is used (e.g. Patent Literature 1). As the Mach-Zehnder type optical modulator, one in which phase difference between two optical waveguides constituting a Mach-Zehnder interferometer changes nonlinearly with respect to an applied voltage is known. In such Mach-Zehnder type optical modulator, a bias electrode to which a bias voltage is applied and a modulation electrode to which a data signal is applied are formed on one or both of the two optical waveguides.
Another example where the bias voltage is applied to the optical waveguide is also known (e.g. Patent Literature 2). In this example, an input light is split to two optical waveguides and the split lights propagating through each optical waveguide are multiplexed to output a modulated light. The bias voltage supplied to at least one optical waveguide in the two optical waveguides is controlled according to a wavelength of the input light. Further, a phase of the modulated light is controlled by a phase device voltage according to the wavelength of the input light.
A multivalued optical signal transmitter configured by using a Mach-Zehnder modulator (Patent Literature 3) is also introduced.
Meanwhile, for example, in an optical communication system in conformity with standards such as SFP (Small Form-Factor Pluggable) and XFP, use of a pluggable optical module has been developed. The pluggable optical module is an optical transceiver that is insertable into and removal from a socket of an optical communication apparatus. When performing a control of the pluggable optical module, the pluggable optical module receives control information from the optical communication apparatus serving as a host side. Then, operation switching and changing of the pluggable optical module are performed according to the received control information.